Dental implants are an increasingly popular option for patients with missing teeth due to excessive decay, periodontitis, or accidents causing physical displacement and the like. Oral rehabilitations supported by dental implants provide an attractive alternative to mucosally supported dentures because they provide more stability and comfort during chewing, allowing patients to resume their normal diets. Furthermore they prevent bone loss due to disuse or incorrect loading of the bone by mucosally supported dentures.
In comparison to dentures and the like, however, dental implant procedures involve costly and complex surgical work. More accurately, dental implant procedures generally involve the placement of a dental implant in the underlying jawbone as a foundation, and the subsequent attachment of a prosthetic part to the implant above the gum line. Generally, an osteotomy must be performed to prepare the bone for placement of the implant. The implant is then inserted and fixed into the bone where it serves to hold the dental prosthetic part. The osteotomy and implant placement must be precise to avoid biological and prosthetic complications.
Inaccuracies in placing the osteotomy can damage nearby vital structures such as nerves, blood vessels, sinuses and neighboring teeth, or needlessly destroy bone. This is especially the case when dealing with pterygoid implants, as these implants are placed in the posterior part of the maxilla, an area with reduced visibility and accessibility, where the bone has very low density at the crestal level.
In fact, the steep learning curve and challenging technique is the only disadvantage of the pterygoid implant (Hernandez Alfaro F, 2013), making this therapeutic modality inaccessible for the average surgeon. Nevertheless, the advantages are numerous: bone grafts (sinus floor elevations) are avoided, maxillary sinus integrity is maintained, predictable results, can be executed under local anesthesia, prosthetic cantilevers are avoided, low morbidity, immediate loading of these implants is possible (drastically reducing treatment time from 6 or 9 months to less than 24 hours). Furthermore, while the morphology of the alveolar crest is highly variable due to atrophy and resorption, the anatomy of the buttress formed by the maxilla, the pyramidal process of the palatine bone and the pterygoid apophysis of the sphenoid bone is relatively constant and implant placement is therefore commonly performed under very specific angles.
Improper placement of the implant osteotomy may cause complications during the implant procedure. If the osteotomy is not placed in the proper position in the jawbone, further drilling may be necessary and primary implant stability may become problematic, endangering implant integration. Even more troublesome, if bone has been mistakenly removed, new bone may have to be grafted or added to the site and allowed to heal for 3-6 months before a new attempt can be made.
Positioning mistakes also require additional office visits by the patient, additional time before loading of the implants with the bridge or prosthesis, and unnecessary discomfort. For this reason, it is highly desirable to reduce the risk of drilling in an incorrect position.
Many tools and methods exist for increasing the accuracy, reliability, and ease with which a surgeon can perform the drilling operation. The most popular technique remains free-hand alignment. In the case of free-hand drilling, a surgeon draws upon his or her experience to determine the proper trajectory and final location of the implant. Because it is difficult to fully inspect the site, especially in the case of pterygoid implants, the surgeon typically has great difficulty in determining the proper position and angulation of the drill in this initial step, even after making a flap.
Model-based or lab-based methods allow improved positioning by allowing less invasive surveying of the implant site. This method also provides for transferring of the measurements from the cast to the actual site. An example of the prior art is U.S. Pat. No. 7,086,860 to Schuman et al. The Schuman method involves using tools to determine the size, angles, and positions for the dental implant on a model cast. The cast is cut to determine the bone position. A graphic is then drawn on the model and tools are used to transfer the placement information of the graphic to the implant site. In the laboratory, the buccal-lingual (“BL”) volume of bone is derived from the subtraction of the tissue depth as measured in the mouth through bone sounding. If the anatomy is followed, an accurate reflection of the available bone volume for implant placement may be determined. The mesio-distal (“MD”) positioning of the implant is derived from the transpositioning or translation of information from a radiograph onto the cast.
The above method has several limitations. The MD positioning in the lab is only an estimate and is not verifiable until transferred to a model and the mouth. Also, this method only allows the surgeon to practice drilling on a model and does not assist with transferring or accurately mapping the determined drilling position from the model back to the implant site. This technique is not possible for pterygoid implants as sound soft tissue references for bone sounding are not available in the soft palate. Furthermore, bone sounding in this area would be very painful and not complication-free.
U.S. Pat. No. 5,556,278 to Meitner is directed to a template to allow a surgeon to more accurately transfer the drilling location determined on the model to the implant site in the mouth. Meitner describes a tooth setup molded around the implant site and then placed on a cast model. The surgeon then drills through the setup. A guide post is inserted through the osteotomy, and a sleeve is inserted over the guide post. A resin is then placed over the entire site with a separating medium between the resin and model. Once the resin dries, the resin is removed and can be used as a template to transfer the exact location from the model to the implant site. Further, the guide sleeve may act as a radiographic marker so the surgeon can determine the location and trajectory of the osteotomy to be made in the bone by taking an X-ray with the template in place in the mouth.
Although the Meitner apparatus allows for relatively precise transfer of a drill location from a model to the implant site, errors still arise due to variations between the model and implant site. Whereas lateral errors might be acceptable for short and straight implants, they become problematic in the case of pterygoid (long and angulated) implants, more in particular at the implant apex due to angular deviations. Also, in the edentulous patient precise repositioning is troublesome. Further, the surgeon may decide on a position using the model and later reconsider when examining the X-ray with the template and sleeve positioned at the implant site. In this situation, the template must be formed again from the start and the patient will be required to make extra visits to the office, have further X-rays done and wait longer.
Another technique is based upon determining a trajectory for the drill using tools and aids and then translating the trajectory information to the implant site. An exemplar of such a technique is U.S. Pat. No. 5,015,183 to Fenick. Using X-rays, the surgeon determines where the implant should be positioned in the bone and then uses bushings to help guide the drill bit. Fenick also creates a radiology stent that includes an opaque grid. The stent, without any drill bushings, is X-rayed while in the patient's mouth. The stent is then placed over a model of the patient's jaw where the grid provides a frame of reference that helps in manually positioning a drill bit relative to the model jaw. A hole is drilled into the model, and the resulting hole helps align a drill bushing relative to the model. Next, a cast is created over the model to capture the drill bushing. The cast, with the drill bushing, is then placed in the patient's mouth to help guide the drill bit that drills a hole into the patient's jawbone. With the Fenick system, some positional accuracy may be sacrificed because the drill bushing is aligned to a model rather than being aligned directly to the patient's actual jaw.
In more recent years, computers and sophisticated peripheral imaging equipment have caused the positioning of implant systems to become far more sophisticated. Using Computed Tomography one can construct detailed computer models such as computer aided drafting (CAD) drawings. The computer allows technicians and surgeons to experiment with many different positions and trajectories in three-dimensional computer space. A computer also allows a user to calculate the exact trajectory for the drill. Moreover, once the model is constructed and trajectory calculated, the data can be used to prototype a surgical guide for the drill through computer aided manufacturing (CAM). A major drawback is that Computed Tomography Imaging is required, exposing the patient to a radiation dose much higher than with conventional dental radiology (e.g. panoramic X-ray).
Thus, computers in combination with many of the above procedures allow surgeons and technicians great flexibility in planning for the osteotomy and implant procedure. However, once the planning has been converted into the surgical guide, the surgeon is obliged to follow the planned trajectory rigidly or to continue free-handed if the surgical protocol needs adjustment. Translation of the data from the model to the implant site are not always error free, especially when long angulated (e.g.) pterygoid implants are considered. Further practical drawbacks for the use of CAD-CAM guides in the pterygoid area are: the need for longer drills with limited interarch space, bulky bushings and the need for posterior reinforcement of the guide. Besides, such equipment can be extremely costly. Also, sophisticated equipment requires sophisticated technical skills and may be beyond the reach of those with limited technology skills.
Another method for performing implant osteotomies provides a method for readjusting the drill trajectory directly in the mouth. U.S. Pat. No. 7,097,451 to Tang describes a thermoplastic surgical template that allows adjustment after initially setting a drill position. The Tang template includes a base and a drill guide. The alignment of the drill guide may be determined using conventional methods. Alternatively, the template may be fastened in the mouth without setting an initial drill position.
The Tang template is constructed of a thermoplastic chosen with thermo-properties such that it can be heated to a state whereupon it can be molded. The thermoplastic then hardens when it cools. Thus, the surgeon can place the template, heat the template, readjust the drill guide with a specified tool, and then allow it to harden at the determined position. This process minimizes the number of office visits and steps in the osteotomy procedure. Surgeons can easily adjust the template at will without going through lots of steps or fabricating procedures.
Although the Tang template allows a surgeon to combine modeling with relatively accurate translation of the data to the implant site, such templates and methods lack readjustment control. The surgeon can readjust the template at the mouth site, but readjustment amounts to free-hand alignment. Once the thermoplastic is heated to a moldable state, the template flows freely in all directions. Essentially, the surgeon must reposition the drill guide in free space, meaning, in three dimensions with 360° of rotation. Additionally, the abutment and temporary crown can only be made after the surgical guide has been approved clinically because of the liberal readjustment procedure. Similar to the other methods described, the Tang method does not provide a controllable and quantifiable method of positioning relative to a dental cast.
Some other documents have tried to provide a device for positioning dental implants but fail to do so however for the very unique situation for placing pterygoid dental implants. For instance, the Korean patent application KR 2013/0127319 A provides a type of drill guide which has two legs defining a direction for the drill to burrow into the jaw. However, as can be seen from the figures of the document, and especially in FIGS. 2 and 3 of the document, the device proposed in the application uses an abutment with two legs to embrace the drill (or part of a drill pathway) and to angle this pathway correctly. In said FIGS. 2 and 3 it is clear that the legs are intended to rest upon the gum tissue and underlying jawbone, and make no use of the unique bone structure in the pterygoid region. It is to be understood that, in the case of dental reconstruction such as placing and/or drilling for a pterygoid dental implant, this gum tissue is very likely to be deformed and thus would provide a variable base for the device for every patient. Even the slightest deformation of this base for the device would shift the drilling angulation which, as is known by one skilled in the art, could easily ruin the operation, causing an incorrect osteotomy and thereby requiring the grafting of new bone material and subsequent repeat of the original operation to create the osteotomy in the first place. Furthermore, as can be seen in said FIGS. 2 and 3, the device has no way of securing itself in any except for the steady hand of the user. Lastly, the application makes no mention of the use of this device for the placement of pterygoid dental implants (or the drilling therefor) and, from what can be seen from the angulation of the drill in FIG. 3, is not intended for such practices.
In a second document, US 2010/151411 A1, a similar device is provided as before, wherein the abutment and the two legs extend and form a lower region. Again, the abutment and the legs are meant to embrace a drill or shape a pathway for a drill, as can be seen in FIGS. 6 and 7 of the document for instance, by resting on the gum tissue and underlying jawbones. The lower region formed is configured to fit into a preformed drill hole, in order to steady the positioned device better and thereby provide a secure guide or pathway for the drill to perform further drilling (typically osteotomies are made by several subsequent drilling operations to either burrow deeper or to perform more delicate operations). The device therefore not only fails to be able to perform the initial action of functioning as a drill guide for a first drilling operation, as it needs a preformed osteotomy or a template (or drill jig) in order to secure the lower end of the abutment and the legs therein. These templates are often invasively secured (bone-supported CAD-CAM surgical guides). If they are mucosally supported, they often lack precision due to fixation errors and in case of pterygoid implants result in a magnification of angular deviations into extensive lateral apical errors. Lastly, and again, the proposed device would not be fit for the placement of pterygoid dental implants (or the drilling therefor) as from said FIG. 7, it is clear that the angulations of the pathway for the drill are incorrect, even more so as the application makes no mention of the use of the device for pterygoid dental implants. As known by one skilled in the art, the placement of pterygoid dental implants is much more delicate than other dental implants, as both the location is difficult to reach and the angulation needs to be exact.
In light of the forgoing, it would be beneficial to have a method and device for placing a pterygoid dental implant which overcomes the above and other disadvantages of known implant positioning systems and methods. What is needed is an improved method and apparatus for determining the ideal drilling trajectory that would allow accurately and repeatably performing a pterygoid dental implant procedure.